Involvement of STH7 in light-adapted development in <i>Arabidopsis thaliana</i> promoted by both strigolactone and karrikin
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Strigolactones (SLs) and karrikins (KARs) regulate photomorphogenesis. GR24, a synthetic SL and KAR<sub>1</sub>, a KAR, inhibit the hypocotyl elongation of <i>Arabidopsis thaliana</i> in a weak light. GR24 and KAR<sub>1</sub> up-regulate the expression of <i>STH7</i>, encoding a transcription factor belonging to the double B-box zinc finger subfamily. In this study, we used <i>STH7</i>-overexpressing (<i>STH7ox</i>) lines and functionally defective <i>STH7</i> (<i>STH7</i>-<i>SRDX</i>) mutants to investigate roles of SLs and KARs in photomorphogenesis of <i>Arabidopsis</i>. Hypocotyl elongation of <i>STH7</i>-<i>SRDX</i> mutants was less sensitive to both GR24 and KAR<sub>1</sub> treatment than that of wild-type <i>Arabidopsis</i> under weak light conditions. Furthermore, the chlorophyll and anthocyanin content was increased in <i>STH7ox</i> lines when de-etiolated with light and GR24-treated plants had enhanced anthocyanin production. GR24 and KAR<sub>1</sub> treatment significantly increased the expression level of photosynthesis-related genes <i>LHCB1</i> and <i>rbcS</i>. The results strongly suggest that SL and KAR induce photomorphogenesis of <i>Arabidopsis</i> in an STH7-dependent manner. Strigolactone response is mediated by D14 and KAI2 while karrikin response is mediated by only KAI2.
